The present invention relates to power saving circuits and more particularly to an improved circuit for further saving power of a wireless pointer in a standby state.
Recently, electrical devices having a power saving feature are very attractive to consumers. Typically, such devices are automatically changed to a power saving mode when inoperative for a predetermined period of time. A conventional design for effecting the power saving feature is shown in FIG. 1. A relay or metal oxide semiconductor field effect transistor (MOSFET) 12 is enabled to cut off power 11 under the control of control 14 when a main electrical element 13 is inoperative for a predetermined period of time. When an activation signal is detected by control 14, the relay or MOSFET 12 is again enabled to connect power 11 to the main electrical element 13. In brief, the on/off of the main electrical element 13 is controlled by the control 14. However, power is continuously consumed in the control 14 irrespective of the on or off state of the main electrical element 13. Further, the design of the circuitry is complex. Furthermore, the on/off of the main electrical element 13 is not normal when the operating voltage is low. Thus improvements are needed.
It is an object of the present invention to provide a power saving device mounted in a wireless pointer powered by a source. The power saving device comprises a bias control circuit, a first resistor, a first capacitor, a second capacitor, and a signal generation circuit comprising an NPN transistor, a third capacitor, an inductor, a second resistor, a third resistor, a fourth capacitor and a fifth capacitor. The collector of the NPN transistor is connected to the positive terminal of the source through the third capacitor, while the emitter is connected to one end of the second resistor. The other end of the second resistor is connected to ground. The bias control circuit comprises a switch, a semiconductor means, the first capacitor, and an n-type channel MOSFET. One end of switch is connected to the gate of the n-type channel MOSFET at a first node, while the other end is connected to ground. A cathode of the semiconductor means is connected to the positive terminal of the source, while the anode is in series connection with the first capacitor at first node. The first capacitor is parallel connected to the switch between the first node and ground. The drain of the n-type channel MOSFET is connected to the base of the NPN transistor of the signal generation circuit. One end of the first resistor is connected to the positive terminal of the source, while the other end is in series connection with the second capacitor at a second node. The other end of the second capacitor is connected to ground. When the wireless pointer is inoperative for a predetermined period of time, the switch is automatically opened to cause the leakage current of the reverse biased semiconductor means to charge the first capacitor. Also, once the switch is operable, it closes to cause the first capacitor to discharge completely so as to cut off the n-type channel MOSFET. The charging and discharging decrease the current consumption of the wireless pointer during standby to a minimum.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description taken with the accompanying drawings.